An organization, such as a company or a group of companies, may use a virtual private network (VPN) for secure communications over a public network. Failures that affect the reliability of the VPN access circuit may occur anywhere from a user's premises through the connection path to the VPN-provider network, and may be difficult to diagnose.
For example, access problems may reside at various levels in the seven layer open systems interconnection (OSI) model of computer network communication and failures of electronic components, including passive components such as cables, may surface in different communication layers. Physical layer 1 problems can occur at the cabling and signaling interface level where connections are established between network devices. Logical data link layer 2 issues may cause data errors associated with the protocols used on the access circuit. Network layer 3 problems may cause routing errors. Cross-layer interactions can complicate the identification of or otherwise mask the root cause of a component failure.
Users can access a VPN network using private lines provided by a VPN-provider, a local exchange carrier, or another alternate access provider. These private lines can be, for example, a 64 kbps circuit conforming to the digital signal 0 (DS-0) telecommunications standard, a line using NxDS-0, a 1.544 Mbps circuit using the digital signal 1 (DS-1) format, a line using NxDS-1, or the like. In many user access circuits, the lines are multiplexed into higher order facilities once they enter an access provider's network and subsequently enter the VPN provider's network. This access path, along with the access paths of many other customers, typically terminates on an optical communication hierarchy level X (OC-X) port on a gigabit switch router serving as an access point to the VPN-provider network. Consequently, when a user reports a problem in connecting to a VPN, the location of the failure causing the problem is typically not easy to determine. For example, a failure may be occurring with customer premises equipment (CPE), or with a local exchange carrier (LEC), or with the VPN provider. Due to the complexity of a customer network system, variability of equipment used, and use of different access alternatives, it may be quite time-consuming for a VPN provider to pinpoint the cause of a problem.